In a process of producing a CCD/CMOS image sensor, an immersion treatment using a solvent, an alkaline solution, or the like is performed. In order to prevent an element from being deteriorated or damaged by such a treatment, a protective film having resistance to the treatment is provided on a surface of the element. Such a protective film is required to have performances such as transparency, high heat resistance and light resistance, prevention of deterioration such as coloration over an extended period of time, and excellent solvent resistance and alkali resistance (Patent Document 1). In recent years, higher definition of the CCD/CMOS image sensor requires improvement in sensitivity of the sensor. When the protective film is formed on a color filter to efficiently concentrate light from a microlens to a light reception portion, the protective film is required to flatten a level difference that is formed on an underlying substrate (Patent Documents 2 to 4). From such a protective film, a microlens is also produced.
A known method for producing a microlens for a CCD/CMOS image sensor is an etch back method (Patent Documents 5 and 6). In the method, a resist pattern is formed on a resin film for a microlens that is formed on a color filter, and then reflowed by heat treatment, forming a lens pattern. The resin film for a microlens as an underlayer is subjected to an etch back process using, as an etching mask, the lens pattern formed by reflowing the resist pattern to transfer the lens pattern shape to the resin film for a microlens. Thus, a microlens is produced.
On the other hand, in a case of conventional pigment dispersion, it is difficult to further improve resolution of a color filter for a CCD/CMOS image sensor. The conventional pigment dispersion has a problem such as occurrence of color unevenness due to coarse and large particles of the pigment. Therefore, the conventional pigment dispersion is not suitable for applications requiring a fine pattern, such as a solid-state imaging element. Accordingly, a technique using a dye instead of the pigment dispersion has been proposed (Patent Document 7). However, the technique has difficultly when applied to a color filter using a dye in which decomposition is generally started at about 180° C. (Patent Document 8) since the conventional thermosetting protective film is baked at a temperature of 180° C. or higher.